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Measuring complexity in soil ecosystems Monika Gorzelak November 24th 2014 Objectives • • • • How can I ask a CAS question in my research? Soil is complex Should behave as a complex adaptive system Explore whether that is measurable in my experiments/research Outline • • • • • Revisit “response diversity” Historical context Tilman Cedar Creek Current theory Introduction to mycorrhizal networks My experiment(s) + CAS Response diversity Definition • Diversity of responses to environmental change among species that contribute to the same ecosystem function • Diversity within functional groups is important to the adaptive capacity of ecosystems; not just species richness Concepts of diversity in plant ecosystems • Tilman 2001 • Hector 1999 • Large scale field experiments that manipulated diversity and measured fitness outcomes • Debate Cedar Creek • Long term experiment • Temperate grasslands, in Minnesota • 16 species, chosen at random into plots in increasing species richness • Measure productivity (biomass) • Increased diversity = increased productivity BIODEPTH • • • • • Europe experiment Same design, 32 plants 8 sites across Europe Hector et al. (2002) Same results: increased diversity results in increased productivity (biomass) (Loreau, 2010) Mechanisms • Complementarity effect: functional niche complementarity, permanent association of species leads to better collective performance • Selection effect: trait variation as initial effect upon which selective process promotes dominance of a particular species • Both at work (Loreau et al. 2001); complementarity more likely (Cardinal et al. 2007) What functions? • Root depth and architecture (Dimitrakopoulos and Schmid 2004) • Nutrient use efficiency (van Ruijen and Berendse 2005) • Increase input and retention of nitrogen (Fargione et al. 2007) • ***grasslands only! Bonfante and Anca 2009 More functions, more interactions Mutualisms • Nitrogen-fixing bacteria (classic example affecting plant diversity, fix nitrogen, facilitate co-existence of other species by generating a nutrient source) • Mycorrhizas. Symbiosis between soil fungi and plant. Plant provides fixed carbon, soil fungus provides mineral nutrient uptake Microscopic structure Colonized root tips • Potential for different types of connections because different species Scales of complexity in soil • Spatial – Roots create heterogeneous structure* – Networks • Temporal – Within a trophic level – Between trophic levels (different time scales apply) Root architecture Networks (Beiler et al. 2010) Scale-free network (Beiler et al. 2010) Temporal (within trophic level) • Behaviour* (within life span, quick changes) • Adaptation (positive/negative feedbacks) – Expression of genes to exploit resources – Improve fitness – Adaptive niche construction (Callahan 2014), vs. homogeneous medium environmental modification • Evolution (“permanent” changes to genome) – Longer term Growth curve example Medium term (mal) adaptation Adaptive niche construction • “Opposite” of a growth curve experiment • More likely in a heterogeneous environment • Modification of a local environment to confer fitness advantage, passing the local improved environment onto offspring • Recently demonstrated in a lab setting using bacteria (easier to do with bacteria because they have short generation times) Soil trophic levels • • • • • • 1st level: primary producers (plants) 2nd level: decomposers, mutualists, pathogens 3rd level: shredders, predators, grazers 4th level: higher level predators (carni) 5th level: even higher level predators (?) Also: food webs, organisms can play at different levels (nematodes eat fungi and are eaten by other fungi...next slide) Fungi eat nematodes! © George L. Barron Temporal scales across trophic levels • Plants interact with mycorrhizas (2 trophic levels) • Bacteria interact with both • Reaction times differ between these 3 components (scale: years, months, days) • (Food webs: there are other players, I’m ignoring them) Seasonal changes in fungi (Pickles et al. 2010) My project: what we know • Douglas-fir connect with mycorrhizas which form networks • Douglas-fir can transfer resources and signals through its mycorhizal network • Douglas-fir preferentially transfers carbon to kin • Douglas-fir transfers defense signals via the mycorrhizal network in response to herbivory My project: what we want to know • Do Douglas-fir transfer defense signals preferentially to kin in response to herbivory? • Need to look at 3 factors: – Mycorrhizal network (yes and no) – Kin vs stranger – Herbivory (insect, manual defoliation, no) Treatments MN defoliation Kin vs stranger insect Kin vs stranger control Kin vs stranger no-MN Kin vs stranger no mesh Kin vs stranger Kin vs stranger Kin vs stranger Kin vs stranger Kin vs stranger MN=mycorrhizal network, using mesh bags that allow fungi to pass, but not roots No-MN=mesh bags exclude roots and fungi, eliminating the mycorrhizal network, while allowing the passage of water and bulk soil flow including nutrients No mesh=control for unknown impacts of including the mesh**changes to spatial heterogeneity I hope to be able to detect by considering complexity of the soil in the design and trying to quantify it under these conditions Design: Two recipient D = donor Rs = recipient, stranger Rs = recipient, kin Design: Tripartite D = donor Rs = recipient, stranger Rs = recipient, kin Thoughts on design • Tripartite is more complex • Should I expect different results? Its essentially the same experiment... • Dilution of label added to Donor • Change to the spatial heterogeneity of the soil structure (can I see this change by monitoring the bacteria...if they change, will they impact the system and possibly alter responses to treatments?) Complexity in soil: Relevant concepts • Spatial heterogeneity causes adaptive radiation in bacteria (increase diversification) • Priority effects (first bacteria arriving takes priority, impacts habitat in the future) • Time-scale differential between plants, fungi, and bacteria Apply treatments: Herbivory, mycorrhizal networks Bacteria • Productivity (measure biomass) • Diversity • species diversity • Functional diversity • Time-scale comparisons •Bacteria at start •Bacteria at finish Diversity and Productivity • Aboveground plant diversity unchanged • Soil spatial structure is altered, allowing for adaptive radiation • Parallel to Tilman: will productivity increase with increased diversity (in bacteria rather than plants?) • Plant stress response have different effects on bacterial community systems (is high diversity system more resilient?) • Will kin vs stranger change the diversity/productivity of bacteria in the system? Questions • Does the bacterial community change in response to – the presence/absence of a mycorrhizal network? – herbivory (with and without a mycorrhizal network)? – Density of seedlings (and therefore changes to root architecture)? – Can these changes be seen temporally over the duration of the experiment? – If layered on top of the original experiment, can these measures inform signal transfer through a MN? Thoughts on measuring complexity? • What should I add? • Is there a better measure of soil complexity (bacteria will be most responsive)? • Change the experiment to include explicit measures of complexity • Do a separate experiment to tease out the factors – Consider no plant pot, single plant pots etc Functional diversity in bacteria • Too much going on in the design? Simplify with a lab experiment? • mimic Tilman experiment, but upside down. Keep above-ground constant, inoculate the soil with known species, use fake roots, fake soil (simplify the system), look for productivity increases and changes in diversity The end.